Soft start circuit

Abstract

The invention provides a soft start circuit, and relates to the technical field of integrated circuits, the soft start circuit comprises an on-off control circuit and a voltage slow-rising circuit, the on-off control end of the on-off control circuit is connected with the charging control end of the voltage slow-rising circuit, and the voltage output end of the voltage slow-rising circuit is connected with an external device to be started; and the on-off control circuit is used for controlling the intermittent conduction of the charging control end of the voltage slow-rising circuit so as to perform slow charging and provide slowly-rising starting voltage for the to-be-started device to realize soft start. The beneficial effects are that the current of the constant current power supply in the voltage slow-rising circuit does not need to be very small, and normal work can be ensured under the condition of high temperature or other large interference. The soft start circuit can work normally in a high-temperature or large-interference occasion, so that the reliability of the whole circuit is improved, and the circuit has the characteristics of simple structure, small occupied layout area, good expandability, high reliability and the like, and can be widely applied to analog integrated circuits needing the soft start circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to a soft start circuit. Background Art

[0002] With the continuous development and advancement of semiconductor technology, many integrated circuits are now widely implemented using low-voltage process technologies. These circuits are extremely sensitive to input voltage. Any input voltage exceeding the rated value can damage these circuits. Therefore, the power output or power conversion integrated circuits that power these circuits require a soft-start mechanism during startup to ensure that the output voltage rises slowly and smoothly, effectively preventing the output voltage from exceeding the rated value.

[0003] Soft-start circuits can be implemented in a variety of ways, primarily categorized as analog and digital. Digital soft-start circuits use digital signals to gradually increase a reference voltage, thereby gradually increasing the output voltage. This implementation can take many forms. For example, the reference voltage can be divided by multiple resistors to achieve a gradual increase in the output voltage. However, this method requires a large number of resistors and precise matching between them, often requiring complex wiring, even multi-layer wiring, which consumes a large layout area and hinders high integration.

[0004] Analog soft-start circuits, on the other hand, primarily achieve soft-start by charging a capacitor with a resistor or constant current. This approach works well for short soft-start times. However, if a longer soft-start is required, larger resistors or capacitors are required, which also occupies a larger layout area and hinders integration. Smaller capacitors, however, require a smaller charging current. However, in high-temperature or high-noise environments, the capacitors are prone to leakage, causing soft-start failure and circuit malfunction. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a soft start circuit, including an on-off control circuit and a voltage ramp-up circuit, wherein the on-off control end of the on-off control circuit is connected to the charging control end of the voltage ramp-up circuit, and the voltage output end of the voltage ramp-up circuit is connected to an external device to be started; the on-off control circuit is used to control the intermittent conduction of the charging control end of the voltage ramp-up circuit to perform slow charging, thereby providing the device to be started with a slowly rising starting voltage to achieve soft start.

[0006] Preferably, the on-off control circuit includes: a ring oscillation circuit, the signal output end of the ring oscillation circuit is connected to the input end of a signal inverter, and the signal output end of the ring oscillation circuit and the output end of the signal inverter are connected to the charging control end of the voltage ramp-up circuit.

[0007] Preferably, the ring oscillation circuit includes: three inverters whose input and output ends are connected in series in sequence, a capacitor is connected between the output end of the first inverter and the input end of the second inverter, and the output end of the third inverter is connected to the input end of the signal inverter.

[0008] Preferably, the voltage ramp-up circuit includes: a constant current power supply, the power supply end of the constant current power supply is respectively connected to the source of the first PMOS tube and the source of the second PMOS tube, and the gate of the first PMOS tube and the gate of the second PMOS tube are connected to the on-off control end of the on-off control circuit; a soft start capacitor, the upper plate of the soft start capacitor is connected to the drain of the second PMOS tube, the lower plate of the soft start capacitor is connected to the drain of the first PMOS tube and the drain of the first NMOS tube, the source of the first NMOS tube is grounded, and the drain and gate of the first NMOS tube are short-circuited; a second NMOS tube, the gate of the second NMOS tube is connected to the upper plate of the soft start capacitor, the drain of the second NMOS tube is connected to the voltage source, and the source of the second NMOS tube is connected to the external device to be started.

[0009] Preferably, it further includes a voltage divider circuit, which is connected between the voltage output end of the voltage ramp-up circuit and the external device to be started, and is used to adjust the starting voltage output by the voltage ramp-up circuit to adjust the soft start time.

[0010] Preferably, the voltage divider circuit includes: a first resistor, one end of the first resistor is connected to the voltage output end of the voltage ramp-up circuit and the first filter capacitor, the other end of the first resistor is respectively connected to one end of the second resistor and one end of the third resistor, and the other end of the third resistor is connected to the second filter capacitor and the external device to be started.

[0011] Preferably, a third NMOS tube is further included, wherein the drain of the third NMOS tube is connected to the upper plate connected to the soft-start capacitor, the source of the third NMOS tube is grounded, and the gate of the third NMOS tube receives a discharge enable signal.

[0012] The above technical solution has the following advantages or beneficial effects: the on-off control circuit controls the intermittent conduction of the charging control terminal of the voltage ramp circuit to perform slow charging, providing a slowly rising starting voltage to the starting device to achieve soft starting. Therefore, the current of the constant current power supply in the voltage ramp circuit does not need to be very small, and normal operation can be guaranteed under conditions of high temperature or other significant interference. The soft start circuit can operate normally even in high temperature or high interference conditions, thereby improving the reliability of the entire circuit. The circuit has the characteristics of simple structure, small layout area, good scalability, and high reliability, and can be widely used in analog integrated circuits requiring soft start circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is an existing conventional soft start circuit; Figure 2 FIG1 is a structural diagram of a soft start circuit in a preferred embodiment of the present invention; Figure 3 Schematic diagram of the structure of the on-off control circuit in a preferred embodiment of the present invention; Figure 4 This is a schematic structural diagram of a voltage ramp-up circuit and a voltage divider circuit in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0014] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. The present invention is not limited to this embodiment, and other embodiments may also fall within the scope of the present invention as long as they conform to the gist of the present invention.

[0015] In a preferred embodiment of the present invention, based on the above-mentioned problems existing in the prior art, a soft start circuit is provided, including an on-off control circuit 1 and a voltage ramp-up circuit 2, the on-off control end of the on-off control circuit 1 is connected to the charging control end of the voltage ramp-up circuit 2, and the voltage output end of the voltage ramp-up circuit 2 is connected to an external device to be started 3; the on-off control circuit 1 is used to control the intermittent conduction of the charging control end of the voltage ramp-up circuit 2 to perform slow charging, and provide a slowly rising starting voltage to the device to be started 3 to achieve soft start.

[0016] like Figure 1The figure shows a conventional soft-start circuit in the prior art, in which I0 is a constant current source, C0 is a soft-start capacitor, and Q0 is an enable transistor. When the circuit is not operating, Q0 is turned on to discharge C0. When the circuit is operating, Q0 is turned off, and the constant current source I0 charges the soft-start capacitor C0, causing the output voltage Vo to slowly increase, achieving the soft-start function. Due to the area constraints of the integrated circuit, the capacitor C0 cannot be too large, so the constant current source current can only be reduced to achieve a slow increase in Vo. However, if the current is too small, the leakage current of Q0 may be greater than the constant current source current at high temperatures or under large interference, making it impossible for the capacitor C0 to complete charging and the soft-start circuit to malfunction. If the constant current source current is increased, the area of ​​the soft-start capacitor must also be increased to achieve the soft-start function.

[0017] In view of the above problems existing in the prior art, the present invention provides a highly reliable soft start circuit. Figure 2 The circuit shown includes an on-off control circuit 1 and a voltage ramp circuit 2. The on-off control circuit 1 controls the intermittent conduction of the charging control terminal of the voltage ramp circuit 2 to perform slow charging, providing a slowly rising starting voltage to the starting device 3 to achieve soft starting. Therefore, the current of the constant current power supply in the voltage ramp circuit 2 does not need to be very small, and normal operation can be guaranteed under conditions of high temperature or other significant interference. The soft start circuit can operate normally in high temperature or high interference conditions, thereby improving the reliability of the entire circuit. The circuit has the characteristics of simple structure, small layout area, good scalability, and high reliability, and can be widely used in analog integrated circuits that require a soft start circuit.

[0018] In a preferred embodiment of the present invention, the on-off control circuit 1 includes: a ring oscillation circuit 11, the signal output end of the ring oscillation circuit 11 is connected to the input end of a signal inverter I4, and the signal output end of the ring oscillation circuit 11 and the output end of the signal inverter I4 are connected to the charging control end of the voltage ramp-up circuit 2.

[0019] In a preferred embodiment of the present invention, the ring oscillator circuit 11 includes: three inverters I1, I2, and I3 whose input and output ends are connected in series in sequence, a capacitor C1 is connected between the output end of the first inverter I1 and the input end of the second inverter I2, and the output end of the third inverter I3 is connected to the input end of the signal inverter I4.

[0020] Specifically, such as Figure 3As shown, the on-off control circuit consists of four inverters and a capacitor C1. Inverters I1, I2, and I3, along with capacitor C1, form a ring oscillator circuit, outputting CLK1. Signal inverter I4 outputs CLK2, which has an opposite phase to CLK1. The ring oscillator circuit outputs a high-level clock signal CLK1 with a very low duty cycle, D. CLK2, the inverted signal of CLK1, is a low-level clock signal with a very low duty cycle, D. When signal CLK2 is low, the charge control terminal of the voltage ramp circuit is turned on for charging. This intermittent conduction mode controls slow charging, providing a slowly rising starting voltage to the device to be started, achieving soft start.

[0021] In a preferred embodiment of the present invention, the voltage ramp-up circuit 2 includes: a constant current power supply I5, wherein the power supply end of the constant current power supply I5 is respectively connected to the source of the first PMOS tube Q1 and the source of the second PMOS tube Q2, and the gate of the first PMOS tube Q1 and the gate of the second PMOS tube Q2 are connected to the on-off control end of the on-off control circuit 1; a soft start capacitor C2, wherein the upper plate of the soft start capacitor C2 is connected to the drain of the second PMOS tube Q2, the lower plate of the soft start capacitor C2 is connected to the drain of the first PMOS tube Q1 and the drain of the first NMOS tube Q3, the source of the first NMOS tube Q3 is grounded, and the drain and gate of the first NMOS tube Q3 are short-circuited; a second NMOS tube Q4, wherein the gate of the second NMOS tube Q4 is connected to the upper plate of the soft start capacitor C2, the drain of the second NMOS tube Q4 is connected to the voltage source VDD, and the source of the second NMOS tube Q4 is connected to the external device 3 to be started.

[0022] Specifically, in this embodiment, Figure 4 As shown, the voltage ramp-up circuit 2 is composed of a constant current power supply I5, a first PMOS transistor Q1, a second PMOS transistor Q2, a first NMOS transistor Q3, a second NMOS transistor Q4, and a soft-start capacitor C2.

[0023] The constant current power supply I5 provides a stable and reliable constant current with a current value of I. The first PMOS transistor Q1 is turned on or off by CLK1, and the second PMOS transistor Q2 is turned on or off by CLK2.

[0024] The soft-start capacitor C2 has a capacitance of C, and its upper plate serves as a voltage output to control the gate of the second NMOS transistor Q4.

[0025] The source of the first NMOS transistor Q3 is grounded, and the gate and drain of the first NMOS transistor Q3 are short-circuited and connected to the lower plate of the soft-start capacitor C2.

[0026] CLK1 and CLK2 are anti-phase signals, causing the first PMOS transistor Q1 and the second PMOS transistor Q2 to be alternately turned on. When the second PMOS transistor Q2 is turned on, the soft-start capacitor C2 is charged. Since CLK2 is a low-level signal with a very small duty cycle, the charging current of the soft-start capacitor C2 is very small. Under the action of CLK1 and CLK2, the first PMOS transistor Q1 and the second PMOS transistor Q2 are alternately turned on, causing the top plate voltage of the soft-start capacitor C2 to gradually increase, and the source voltage of the second NMOS transistor Q4 to gradually increase accordingly, providing a slowly increasing starting voltage to the to-be-started device 3 to achieve soft starting.

[0027] The current for charging the soft-start capacitor C2 is reduced by the conduction time ratio D of the second PMOS tube Q2. Therefore, the current I of the constant current power supply I5 does not need to be very small, and normal operation can be guaranteed under high temperature or other large interference conditions.

[0028] In a preferred embodiment of the present invention, a voltage divider circuit 4 is further included, which is connected between the voltage output terminal A of the voltage ramp-up circuit 2 and the external device to be started 3, and is used to adjust the starting voltage output by the voltage ramp-up circuit 2 to adjust the soft start time.

[0029] In a preferred embodiment of the present invention, the voltage divider circuit 4 includes: a first resistor R1, one end of the first resistor R1 is connected to the voltage output end of the voltage ramp-up circuit 2 and the first filter capacitor C3, the other end of the first resistor R1 is respectively connected to one end of the second resistor R2 and one end of the third resistor R3, and the other end V0 of the third resistor R3 is connected to the second filter capacitor C4 and the external device to be started 3.

[0030] Specifically, in this embodiment, Figure 4 As shown, it also includes a voltage divider circuit 4, which is composed of a first filter capacitor C3, a resistor R1, a resistor R2, a resistor R3, and a second filter capacitor C4.

[0031] The source voltage of the second NMOS transistor Q4 gradually increases, and after being divided by resistors R1 and R2, it is filtered by resistor R3 and second filter capacitor C4 to output a slowly rising voltage, thus realizing the soft-start circuit function. Furthermore, by adjusting the voltage-dividing ratio of resistors R1 and R2, the soft-start time can be further adjusted, thereby increasing the constant current source current or the charging duty cycle, further improving the reliability of the soft-start circuit.

[0032] In a preferred embodiment of the present invention, a third NMOS transistor Q5 is further included, wherein the drain of the third NMOS transistor Q5 is connected to the upper plate of the soft-start capacitor C2, the source of the third NMOS transistor Q5 is grounded, and the gate of the third NMOS transistor Q5 receives the discharge enable signal EN.

[0033] Specifically, in this embodiment, Figure 4 As shown, the third NMOS transistor Q5 is also included. The third NMOS transistor Q5 is a discharge tube. When the circuit is not working, it is turned on to discharge the soft-start capacitor C2.

[0034] It can be seen from all the above embodiments that the soft start circuit of the present invention uses fewer electronic components, has the characteristics of simple structure, small layout area, good scalability, high reliability, etc., and can be widely used in analog integrated circuits that require soft start circuits.

[0035] The above are only preferred embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of this specification and illustrations should be included in the protection scope of the present invention.

Claims

1. A soft start circuit, characterized in that: It includes an on-off control circuit and a voltage ramp-up circuit, wherein the on-off control end of the on-off control circuit is connected to the charging control end of the voltage ramp-up circuit, and the voltage output end of the voltage ramp-up circuit is connected to an external device to be started; the on-off control circuit is used to control the intermittent conduction of the charging control end of the voltage ramp-up circuit to perform slow charging, thereby providing a slowly rising starting voltage to the device to be started to achieve soft starting.

2. The soft start circuit according to claim 1, characterized in that: The on-off control circuit includes: a ring oscillation circuit, a signal output end of the ring oscillation circuit is connected to an input end of a signal inverter, and the signal output end of the ring oscillation circuit and the output end of the signal inverter are connected to a charging control end of the voltage ramp-up circuit.

3. The soft start circuit according to claim 2, characterized in that: The ring oscillation circuit comprises: three inverters whose input and output ends are connected in series in sequence, a capacitor is connected between the output end of the first inverter and the input end of the second inverter, and the output end of the third inverter is connected to the input end of the signal inverter.

4. The soft start circuit according to claim 1, characterized in that: The voltage ramp-up circuit includes: a constant current power supply, wherein the power supply end of the constant current power supply is respectively connected to the source of the first PMOS tube and the source of the second PMOS tube, and the gate of the first PMOS tube and the gate of the second PMOS tube are connected to the on-off control end of the on-off control circuit; a soft start capacitor, wherein the upper plate of the soft start capacitor is connected to the drain of the second PMOS tube, the lower plate of the soft start capacitor is connected to the drain of the first PMOS tube and the drain of the first NMOS tube, the source of the first NMOS tube is grounded, and the drain and the gate of the first NMOS tube are short-circuited; a second NMOS tube, wherein the gate of the second NMOS tube is connected to the upper plate of the soft start capacitor, the drain of the second NMOS tube is connected to a voltage source, and the source of the second NMOS tube is connected to an external device to be started.

5. The soft start circuit according to claim 1, characterized in that: It also includes a voltage divider circuit, which is connected between the voltage output end of the voltage ramp-up circuit and an external device to be started, and is used to adjust the starting voltage output by the voltage ramp-up circuit to adjust the soft start time.

6. The soft start circuit according to claim 5, characterized in that: The voltage divider circuit includes: a first resistor, one end of the first resistor is connected to the voltage output end of the voltage ramp-up circuit and a first filter capacitor, the other end of the first resistor is respectively connected to one end of a second resistor and one end of a third resistor, the other end of the third resistor is connected to a second filter capacitor and an external device to be started.

7. The soft start circuit according to claim 4, characterized in that: It also includes a third NMOS tube, the drain of the third NMOS tube is connected to the upper plate connected to the soft start capacitor, the source of the third NMOS tube is grounded, and the gate of the third NMOS tube receives a discharge enable signal.

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